Re: 3 points from a new user of gsl

[Toby White <tow at theor dot ch dot cam dot ac dot uk>]

Jean-Max Redonnet <jmax.redonnet@meca.insa-tlse.fr> writes:

> Hi,
> 
> I'm a new user of gsl. I plan to use it for managing with vectors and 
> matrices and multidimensional root finding.
> Here is my first impression on this library (be indulgent, i'm not a great 
> hacker,  just a phD in mechanical engineering needing free tools to solve its 
[snip]

> Multidimensional root finding :
> works fine especially with newton algorithm (as expected).
> just a suggestion : It would be nice sometimes to be able to bound each 
> variable. I've not find an easy way to do this in current release. Although 
> this may help the algorithm to find the "right" solution. Is it possible ? Is 
> it reasonnable to imagine this will be possible in future releases?

I do this by transforming the bounded variables onto an infinite space
before applying the solver;
e.g. one of my variables is not allowed to be less than zero, or greater
than 0.74 - so I transform by
tan(((x)-0.37)*M_PI/0.74)
before applying the solver, and afterwards by
atan(x)*0.74/M_PI+0.37.

Similar functions can be dreamt up for more complicated bounds.

Which means the solver doesn't have to care about bounds, but the
value of my variable will never go outside its proper range. 

Toby

-- 
Toby White, University Chemical Lab., Lensfield Road, Cambridge. CB2 1EW. U.K.
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